Field of the Disclosure
The present disclosure relates to wireless communication systems, and more particularly to techniques for collision detection and management in a shared radio frequency spectrum band.
Description of Related Art
Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, single-carrier frequency-division multiple access (SC-FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
By way of example, a wireless multiple-access communication system may operate according to a first radio access technology (RAT), such as LTE, and may include a number of base stations, each simultaneously supporting communication for multiple communication devices, otherwise known as user equipment (UE) devices. A base station may communicate with UEs on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station). A second wireless multiple-access communications system may operate according to a second RAT, such as Wi-Fi, and may include a number of base stations or access points (APs), each simultaneously supporting communication for multiple mobile devices or stations (STAs). APs may communicate with STAs on downstream and upstream links. In some cases both types of communication systems may operate in the presence of one another and may use shared resources.
In a wireless local area network (WLAN), such as Wi-Fi, an AP may communicate with multiple STAs over a shared radio frequency spectrum. The STAs may use contention procedures that include communicating one or more control frames prior to establishing a communication link, such that confirmation of the communication link via exchange of control frames limits interference experienced by nearby communication devices. One example of such techniques include Request to Send (RTS) and Clear to Send (CTS) messaging, where, for example, a STA looking to communicate with another device (e.g., another STA or AP), may first send an RTS frame to the device. Once the recipient device receives the RTS frame, the recipient device may confirm the communication link by sending a CTS frame. After the CTS frame is received by the STA, the STA may then begin transmitting data to the recipient device. In this way, RTS/CTS messaging can reduce frame collisions by enabling a device, such as a STA or AP, to in essence clear the communication path before transmitting data to an AP or STA.
In an LTE network, a base station and a UE may communicate over a dedicated frequency spectrum or over different frequency bands of the radio frequency spectrum (e.g., a dedicated radio frequency band and a shared radio frequency band) of a cellular network. With increasing data traffic in cellular networks that use dedicated (e.g., licensed) radio frequency bands, offloading of at least some data traffic to a shared radio frequency spectrum may provide a cellular operator with opportunities for enhanced data transmission capacity. A shared radio frequency spectrum may also provide service in areas where access to a dedicated radio frequency spectrum is unavailable. An LTE device that utilizes both dedicated and shared frequency spectrum may be considered to be an LTE-Unlicensed (LTE-U) device.
Prior to gaining access to and communicating over a shared radio frequency spectrum, a base station or UE may perform a listen before talk (LBT) procedure to contend for access to the shared radio frequency spectrum. This LBT procedure may be compatible with contention procedures used by Wi-Fi devices to gain access to the shared radio frequency spectrum. An LBT procedure may include performing a clear channel assessment (CCA) procedure to determine whether a channel of the shared radio frequency spectrum is available. When it is determined that the channel of the shared radio frequency spectrum is available, a channel usage beacon signal (CUBS) may be transmitted to reserve the channel. A different UE or base station may receive and decode the CUBS to identify that the channel has been reserved, while a STA or AP may monitor the shared channel (e.g., using energy detection) to determine whether the channel is busy. After identifying the CUBS, other base stations or UEs may utilize resources on the shared channel that are not being used by the transmitting UE. After determining the detected energy is above a threshold, Wi-Fi devices may refrain from transmitting on the channel for a period of time. The use of LTE and Wi-Fi devices in relatively close proximity to one another may result in one RAT impacting channel access opportunities for transmitting devices using another RAT. Thus, it may be desirable to develop techniques to help provide fairness in channel access opportunities for transmitters accessing a shared radio frequency spectrum using different RATs.